Ultrastructure of human ureter

Electrical propagation in the renal pelvis, ureter and bladder

Under normal conditions, following the passage of urine from the collecting duct, the urine is stored briefly in the renal pelvis before being transported through the ureter to the bladder where the urine is stored for a longer time (hours) before being voided through the urethra. The transport of urine from the renal pelvis to the bladder occurs spontaneously due to contractions of the muscles in the wall of the pelvis and ureter. Spontaneous contractions also occur in the detrusor muscle and are responsible for maintaining the bladder shape during the filling phase. These muscle contractions occur as result of electrical impulses, which are generated and propagated through different parts of the urinary tract. The renal pelvis and the ureter differ from the bladder in relation to the origin, characteristics and propagation of these electrical impulses. In the ureter, the electrical impulses originate mainly at the proximal region of the renal pelvis and are transmitted antegradely down the length of the ureter. The electrical impulses in the bladder, on the other hand, originate at any location in the bladder wall and can be transmitted in different directions with the axial direction being the prominent one. In this manuscript, an overview of the current state of research on the origin and propagation characteristics of these electrical impulses in the normal and pathological conditions is provided.

Pacemaker activity in the upper urinary tract

Ureteral peristaltic activity begins with the origin of electrical activity at pacemaker sites. These sites are located in the proximal portion of the urinary collecting system. The 'atypical' smooth muscle cells at these sites fire 'pacemaker' potentials at a frequency higher than the 'driven' action potentials recorded from typical smooth muscle cells. In contrast to typical smooth muscle cells, these atypical pacemaker cells have less than 40% of their cellular area occupied by contractile filaments and demonstrate a sparse immunoreactivity for alpha-smooth muscle actin. Expression of c-Kit, a tyrosine kinase receptor, correlates with the onset of organized ureteral peristalsis in the embryo. Capsaicin-sensitive sensory afferents and the endogenous release of tachykinins and prostaglandins are involved in the maintenance of normal ureteral peristalsis.

Electro-ureterogram: canine study of the electromechanical activity of the ureter

The purpose of this investigation was to study the electromechanical activity of the ureter aiming at characterizing an "electro-ureterogram" that might be of diagnostic significance. Eighteen mongrel dogs were used in this study. Under anesthesia the ureter was exposed and three electrodes (monopolar, silver-silver chloride, 0.8 mm in diameter) were sutured to the ureteric adventitia, 2-3 cm apart. The intraureteric pressure was measured by a scalp vein needle inserted into the ureteric lumen and connected to a pressure transducer. The ureteric electric activity and pressure were recorded 30 min daily for 15 days. The electric activity was also registered after having performed ureteric myotomy in 12 out of 18 dogs. Monophasic negatively deflected slow waves or pacesetter potentials were recorded. Their frequency, amplitude, and velocity were identical in the three electrodes and reproducible. The pacesetter potentials were followed by fast activity spikes or action potentials that occurred randomly and were inconsistent. The action potentials were associated with ureteric pressure increase. After ureteric myotomy, both the pacesetter potentials and action potentials were recorded proximally to the myotomy but not distally to it, indicating a caudal spread of the waves. In conclusion, a normal electro-ureterogram could be characterized. It might show changes in various pathologic conditions of the ureter and could thus be included as an investigative tool in the diagnosis of ureteric diseases.

The architecture of the musculature of the guinea-pig ureter as examined by scanning electron microscopy

The muscular architecture of the guinea-pig ureter at different levels was examined by scanning electron microscopy. In the middle portion of the ureter, bundles of smooth muscle fibers were rather randomly oriented with respect to each other and to the long axis of the ureter, forming an irregular network. The muscle fibers of the upper ureter were mostly circularly oriented with a few outermost longitudinal muscle bundles. In the lower portion, the muscle bundles were predominantly longitudinally oriented overlying a deeper circular muscle layer. At any level examined, individual muscle fibers were about 100 to 150 microns. long and about 5 microns. wide, exhibiting a generally smooth surface. The adjacent muscle fibers were frequently interconnected by small lateral projections. In the pelvic portion, thin and short longitudinal muscle bundles were scattered over the inner circular muscles. Individual muscle fibers were spindle-shaped, about 70 microns. long, and 5 microns. wide at their thickest central portion. They were characterized by a rugged surface with many irregular projections and depressions. These muscle fibers may represent pacemaker cells. The findings were discussed in relation to the peristaltic movement of the ureter.